Ketene methylphenyl

A variety of optically active 4,4-disubstituted allenecarboxylates 245 were provided by HWE reaction of intermediate disubstituted ketene acetates 244 with homochiral HWE reagents 246 developed by Tanaka and co-workers (Scheme 4.63) [99]. a,a-Di-substituted phenyl or 2,6-di-tert-butyl-4-methylphenyl (BHT) acetates 243 were used for the formation of 245 [100]. Addition of ZnCl2 to a solution of the lithiated phos-phonate may cause binding of the rigidly chelated phosphonate anion by Zn2+, where the axially chiral binaphthyl group dictates the orientation of the approach to the electrophile from the less hindered si phase of the reagent. Similarly, the aryl phosphorus methylphosphonium salt 248 was converted to a titanium ylide, which was condensed with aromatic aldehydes to provide allenes 249 with poor ee (Scheme 4.64) [101]. 

The cyclization of bis(2-methylphenyl)ketene to 4-(2-methylphenyl)isochromene, which involves a [l,5]-hydrogen shift, has been observed (72HCA10). 

KETENES, KETENE DIMERS AND RELATED SUBSTANCES] (Vol 14) N-(4-Methylphenyl)-ketemmine [5110-45-2]... 

Methylphenyl chlorothioforniate, 474 Methyl(phenylthio)ketene, 315-316 Methyl propiolatc, 11... 

The dehalogenation of a-haloacyl halides with zinc occurs readily, particularly for the formation of aromatic ketoketenes like methylphenyl-ketene (90%), diphenylketene (95%),and di-p-xenylketene (60%)/ ... 

The high-boiling ketenes are separated from the diphenylacetic anhydride by extraction rather than by distillation in order to avoid a ketene interchange. In this manner, many types of ketoketenes have been formed, including dimethylketene (49%), diallylketene (80%), dibenzyl-ketene (74%), ethylchloroketene CjH5ClC = CO (50%), and methylphenyl-ketene (75%). ... 

Seebach has also studied the utility of esters in organometallic acylation. In this case, preformed ester enolates of 2,6-di(t-butyl)-4-methylphenyl esters (BHT esters) were slowly warmed above -20 C to form the corresponding ketene. If this was done in the presence of an ad tional equivalent of alkyl-lithium the ketene was trapped to give a ketone enolate in high yield. The same reaction failed to give any product when simple esters such as methyl, ethyl or Nbutyl were uscd. Scheme 17 is illustrative of the method. 

The reactions of 2,3-diarylcyclopropenones with dicyanoketene or bis(trifluoromethyl)-ketene -" furnished triafulvenes through [2-f 2] cycloaddition followed by elimination. It is notable that 2,3-diphenylcyclopropenone (24) and 2,3-bis(4-methylphenyl)cyclopropcnone (27) followed different routes with bis(trifluoromethyl)ketene. 3-[Bis(trifluoromethyl)methylene]-1,2-bis(4-tolyl)cyclopropene (28) thus obtained had a large dipole amoment (ji = 1.42 D) comparable to that of 4 (/i = 7.9 D). 

Similarly, a qualitative relation between the chemical behavior and the distortion from ideal C2v symmetry was suggested for a series of lithium ester enolates (Scheme 6.13) [108]. Enolate 1, furthest along the reaction coordinate to ketene, had to be handled at temperatures below -50°C and decomposed rapidly at temperatures higher than -30°C. The two other enolates, 2 and 3, were found to survive in crystalline form at 0°C and at room temperature, respectively. The decomposition occurs most likely through a ketene-like intermediate, whose transient existence was demonstrated by cleaving the lithium enolate of 2,6-di-/ert-butyl-4-methylphenyl-2-methylpropanoate at room temperature in the presence of excess -BuLi. 

Compounds prepared in this way include dibenzyl- (73% yield), diallyl- (80% yield), and methylphenyl-ketene (75% yield). 

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